The IAs point is that they should not have to do that, partly because of first sale doctrine. They bought each ebook, and only lend out that copy, the exact same as libraries do now.
1 bought copy, 1 lend. That’s a fair and simple system that mimics hundreds of years of physical book lending.
Their other point is that the societal good of allowing anyone in the world to educate themselves for free far, far outweigh the value of monetary gain for publishers. Since copyright is intended to help society, their interpretation is the better application of it.